遇见 Kotlin

Bennyhuo

个人介绍

霍丙乾 Bennyhuo

腾讯地图 Android 工程师
Kotlin “布道师”
Kotlin 微信公众号
目前国内第一套 Kotlin 视频教程

最新视频：Kotlin 入门到进阶

http://coding.imooc.com/class/108.html

Kotlin 是什么

Kotlin 官网

静态语言

与 Java 完美兼容
有完美的 IDE 提示
确定的类型给人以安全感

import kotlin.browser.document

/**
 * Created by benny on 4/30/17.
 */

fun main(args: Array<String>) {
    document.writeln("Hello World from Kotlin-js")
}


Observable
    .from("HelloWorld".toCharArray().asIterable())
    .zipWith(
            Observable.interval(1, 1, TimeUnit.SECONDS), 
            { a, b -> "$a, $b" })
    .subscribe(::println)

可以跑在Java 虚拟机上


Observable
    .from("HelloWorld".toCharArray().asIterable())
    .zipWith(
            Observable.interval(1, 1, TimeUnit.SECONDS), 
            { a, b -> "$a, $b" })
    .subscribe(::println)

// ================net/println/kt07/LambdaKt.class =================
// class version 50.0 (50)
// access flags 0x31
public final class net/println/kt07/LambdaKt {


  // access flags 0x19
  public final static main([Ljava/lang/String;)V
    @Lorg/jetbrains/annotations/NotNull;() // invisible, parameter 0
   L0
    ALOAD 0
    LDC "args"
    INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull (Ljava/lang/Object;Ljava/lang/String;)V
   L1
    LINENUMBER 16 L1
   L2
    LINENUMBER 20 L2
   L3
    LINENUMBER 16 L3
   L4
    LINENUMBER 17 L4
   L5
    LINENUMBER 16 L5
    LDC "HelloWorld"
    ASTORE 1
   L6
    ALOAD 1
   L7
    INVOKEVIRTUAL java/lang/String.toCharArray ()[C
    DUP
    LDC "(this as java.lang.String).toCharArray()"
    INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkExpressionValueIsNotNull (Ljava/lang/Object;Ljava/lang/String;)V
   L8
   L9
    LINENUMBER 16 L9
    INVOKESTATIC kotlin/collections/ArraysKt.asIterable ([C)Ljava/lang/Iterable;
    INVOKESTATIC rx/Observable.from (Ljava/lang/Iterable;)Lrx/Observable;
    LCONST_1
    LCONST_1
    GETSTATIC java/util/concurrent/TimeUnit.SECONDS : Ljava/util/concurrent/TimeUnit;
    INVOKESTATIC rx/Observable.interval (JJLjava/util/concurrent/TimeUnit;)Lrx/Observable;
    GETSTATIC net/println/kt07/LambdaKt$main$1.INSTANCE : Lnet/println/kt07/LambdaKt$main$1;
    CHECKCAST rx/functions/Func2
   L10
    LINENUMBER 17 L10
    INVOKEVIRTUAL rx/Observable.zipWith (Lrx/Observable;Lrx/functions/Func2;)Lrx/Observable;
    NEW net/println/kt07/LambdaKt$sam$Action1$75bbf535
    DUP
    GETSTATIC net/println/kt07/LambdaKt$main$2.INSTANCE : Lnet/println/kt07/LambdaKt$main$2;
    CHECKCAST kotlin/jvm/functions/Function1
    DUP
    IFNONNULL L11
    POP
    POP2
    ACONST_NULL
    GOTO L12
   L11
    INVOKESPECIAL net/println/kt07/LambdaKt$sam$Action1$75bbf535.<init> (Lkotlin/jvm/functions/Function1;)V
   L12
    CHECKCAST rx/functions/Action1
   L13
    LINENUMBER 20 L13
    INVOKEVIRTUAL rx/Observable.subscribe (Lrx/functions/Action1;)Lrx/Subscription;
    POP
   L14
    LINENUMBER 22 L14
    LDC 15000
    INVOKESTATIC java/lang/Thread.sleep (J)V
   L15
    LINENUMBER 23 L15
    RETURN
   L16
    LOCALVARIABLE args [Ljava/lang/String; L0 L16 0
    MAXSTACK = 6
    MAXLOCALS = 2

  @Lkotlin/Metadata;(mv={1, 1, 6}, bv={1, 0, 1}, k=2, d1={"\u0000\u0014\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0002\u0008\u0002\u001a\u0019\u0010\u0000\u001a\u00020\u00012\u000c\u0010\u0002\u001a\u0008\u0012\u0004\u0012\u00020\u00040\u0003\u00a2\u0006\u0002\u0010\u0005\u00a8\u0006\u0006"}, d2={"main", "", "args", "", "", "([Ljava/lang/String;)V", "production sources for module kt07_main"})
  // access flags 0x18
  final static INNERCLASS net/println/kt07/LambdaKt$main$1 null null
  // access flags 0x18
  final static INNERCLASS net/println/kt07/LambdaKt$main$2 null null
  // compiled from: Lambda.kt
  // debug info: SMAP
Lambda.kt
Kotlin
*S Kotlin
*F
+ 1 Lambda.kt
net/println/kt07/LambdaKt
*L
1#1,28:1
*E

}


// ================net/println/kt07/LambdaKt$main$1.class =================
// class version 50.0 (50)
// access flags 0x30
// signature <T1:Ljava/lang/Object;T2:Ljava/lang/Object;R:Ljava/lang/Object;>Ljava/lang/Object;Lrx/functions/Func2<TT;TT2;TR;>;
// declaration: net/println/kt07/LambdaKt$main$1<T1, T2, R> implements rx.functions.Func2<T, T2, R>
final class net/println/kt07/LambdaKt$main$1 implements rx/functions/Func2  {


  // access flags 0x1041
  public synthetic bridge call(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
    ALOAD 0
    ALOAD 1
    CHECKCAST java/lang/Character
    ALOAD 2
    CHECKCAST java/lang/Long
    INVOKEVIRTUAL net/println/kt07/LambdaKt$main$1.call (Ljava/lang/Character;Ljava/lang/Long;)Ljava/lang/String;
    ARETURN
    MAXSTACK = 3
    MAXLOCALS = 3

  // access flags 0x11
  public final call(Ljava/lang/Character;Ljava/lang/Long;)Ljava/lang/String;
  @Lorg/jetbrains/annotations/NotNull;() // invisible
   L0
    LINENUMBER 19 L0
    NEW java/lang/StringBuilder
    DUP
    INVOKESPECIAL java/lang/StringBuilder.<init> ()V
    ALOAD 1
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/Object;)Ljava/lang/StringBuilder;
    LDC ", "
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
    ALOAD 2
    INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/Object;)Ljava/lang/StringBuilder;
    INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
   L1
    ARETURN
   L2
    LOCALVARIABLE this Lnet/println/kt07/LambdaKt$main$1; L0 L2 0
    LOCALVARIABLE a Ljava/lang/Character; L0 L2 1
    LOCALVARIABLE b Ljava/lang/Long; L0 L2 2
    MAXSTACK = 2
    MAXLOCALS = 3

  // access flags 0x0
  <init>()V
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
    MAXSTACK = 1
    MAXLOCALS = 1

  // access flags 0x19
  public final static Lnet/println/kt07/LambdaKt$main$1; INSTANCE

  // access flags 0x8
  static <clinit>()V
    NEW net/println/kt07/LambdaKt$main$1
    DUP
    INVOKESPECIAL net/println/kt07/LambdaKt$main$1.<init> ()V
    PUTSTATIC net/println/kt07/LambdaKt$main$1.INSTANCE : Lnet/println/kt07/LambdaKt$main$1;
    RETURN
    MAXSTACK = 2
    MAXLOCALS = 0

  @Lkotlin/Metadata;(mv={1, 1, 6}, bv={1, 0, 1}, k=3, d1={"\u0000\u0018\n\u0000\n\u0002\u0010\u000e\n\u0000\n\u0002\u0010\u000c\n\u0002\u0008\u0002\n\u0002\u0010\u0009\n\u0002\u0008\u0002\u0010\u0000\u001a\u00020\u00012\u000e\u0010\u0002\u001a\n \u0004*\u0004\u0018\u00010\u00030\u00032\u000e\u0010\u0005\u001a\n \u0004*\u0004\u0018\u00010\u00060\u0006H\n\u00a2\u0006\u0004\u0008\u0007\u0010\u0008"}, d2={"<anonymous>", "", "a", "", "kotlin.jvm.PlatformType", "b", "", "call", "(Ljava/lang/Character;Ljava/lang/Long;)Ljava/lang/String;"})
  OUTERCLASS net/println/kt07/LambdaKt main ([Ljava/lang/String;)V
  // access flags 0x18
  final static INNERCLASS net/println/kt07/LambdaKt$main$1 null null
  // compiled from: Lambda.kt
}


// ================net/println/kt07/LambdaKt$sam$Action1$75bbf535.class =================
// class version 50.0 (50)
// access flags 0x30
final class net/println/kt07/LambdaKt$sam$Action1$75bbf535 implements rx/functions/Action1  {


  @Lkotlin/Metadata;(mv={1, 1, 6}, bv={1, 0, 1}, k=3)

  // access flags 0x1012
  private final synthetic Lkotlin/jvm/functions/Function1; function

  // access flags 0x0
  <init>(Lkotlin/jvm/functions/Function1;)V
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    ALOAD 0
    ALOAD 1
    PUTFIELD net/println/kt07/LambdaKt$sam$Action1$75bbf535.function : Lkotlin/jvm/functions/Function1;
    RETURN
    MAXSTACK = 2
    MAXLOCALS = 2

  // access flags 0x1011
  // signature (TT;)V
  // declaration: void call(T)
  public final synthetic call(Ljava/lang/Object;)V
   L0
    ALOAD 0
    GETFIELD net/println/kt07/LambdaKt$sam$Action1$75bbf535.function : Lkotlin/jvm/functions/Function1;
    ALOAD 1
    INVOKEINTERFACE kotlin/jvm/functions/Function1.invoke (Ljava/lang/Object;)Ljava/lang/Object;
    DUP
    LDC "invoke(...)"
    INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkExpressionValueIsNotNull (Ljava/lang/Object;Ljava/lang/String;)V
    POP
    RETURN
   L1
    LOCALVARIABLE this Lrx/functions/Action1; L0 L1 0
    LOCALVARIABLE t Ljava/lang/Object; L0 L1 1
    MAXSTACK = 3
    MAXLOCALS = 2
  // compiled from: Lambda.kt
}


// ================net/println/kt07/LambdaKt$main$2.class =================
// class version 50.0 (50)
// access flags 0x30
// signature Lkotlin/jvm/internal/FunctionReference;Lkotlin/jvm/functions/Function1<Ljava/lang/Object;Lkotlin/Unit;>;
// declaration: net/println/kt07/LambdaKt$main$2 extends kotlin.jvm.internal.FunctionReference implements kotlin.jvm.functions.Function1<java.lang.Object, kotlin.Unit>
final class net/println/kt07/LambdaKt$main$2 extends kotlin/jvm/internal/FunctionReference  implements kotlin/jvm/functions/Function1  {


  // access flags 0x1041
  public synthetic bridge invoke(Ljava/lang/Object;)Ljava/lang/Object;
    ALOAD 0
    ALOAD 1
    INVOKEVIRTUAL net/println/kt07/LambdaKt$main$2.invoke (Ljava/lang/Object;)V
    GETSTATIC kotlin/Unit.INSTANCE : Lkotlin/Unit;
    ARETURN
    MAXSTACK = 2
    MAXLOCALS = 2

  // access flags 0x11
  public final invoke(Ljava/lang/Object;)V
    @Lorg/jetbrains/annotations/Nullable;() // invisible, parameter 0
   L0
    LINENUMBER 20 L0
   L1
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ALOAD 1
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/Object;)V
   L2
   L3
    RETURN
   L4
    LOCALVARIABLE this Lnet/println/kt07/LambdaKt$main$2; L0 L4 0
    LOCALVARIABLE p1 Ljava/lang/Object; L0 L4 1
    MAXSTACK = 2
    MAXLOCALS = 2

  // access flags 0x11
  public final getOwner()Lkotlin/reflect/KDeclarationContainer;
    LDC Lkotlin/io/ConsoleKt;.class
    LDC "production sources for module kt07_main"
    INVOKESTATIC kotlin/jvm/internal/Reflection.getOrCreateKotlinPackage (Ljava/lang/Class;Ljava/lang/String;)Lkotlin/reflect/KDeclarationContainer;
    ARETURN
    MAXSTACK = 2
    MAXLOCALS = 1

  // access flags 0x11
  public final getName()Ljava/lang/String;
    LDC "println"
    ARETURN
    MAXSTACK = 1
    MAXLOCALS = 1

  // access flags 0x11
  public final getSignature()Ljava/lang/String;
    LDC "println(Ljava/lang/Object;)V"
    ARETURN
    MAXSTACK = 1
    MAXLOCALS = 1

  // access flags 0x0
  <init>()V
    ALOAD 0
    ICONST_1
    INVOKESPECIAL kotlin/jvm/internal/FunctionReference.<init> (I)V
    RETURN
    MAXSTACK = 2
    MAXLOCALS = 1

  // access flags 0x19
  public final static Lnet/println/kt07/LambdaKt$main$2; INSTANCE

  // access flags 0x8
  static <clinit>()V
    NEW net/println/kt07/LambdaKt$main$2
    DUP
    INVOKESPECIAL net/println/kt07/LambdaKt$main$2.<init> ()V
    PUTSTATIC net/println/kt07/LambdaKt$main$2.INSTANCE : Lnet/println/kt07/LambdaKt$main$2;
    RETURN
    MAXSTACK = 2
    MAXLOCALS = 0

  @Lkotlin/Metadata;(mv={1, 1, 6}, bv={1, 0, 1}, k=3, d1={"\u0000\u0014\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0000\n\u0002\u0018\u0002\n\u0002\u0008\u0003\u0010\u0000\u001a\u00020\u00012\u0017\u0010\u0002\u001a\u0013\u0018\u00010\u0003\u00a2\u0006\u000c\u0008\u0004\u0012\u0008\u0008\u0005\u0012\u0004\u0008\u0008(\u0006\u00a2\u0006\u0002\u0008\u0007"}, d2={"<anonymous>", "", "p1", "", "Lkotlin/ParameterName;", "name", "message", "invoke"})
  OUTERCLASS net/println/kt07/LambdaKt main ([Ljava/lang/String;)V
  // access flags 0x18
  final static INNERCLASS net/println/kt07/LambdaKt$main$2 null null
  // compiled from: Lambda.kt
  // debug info: SMAP
Lambda.kt
Kotlin
*S Kotlin
*F
+ 1 Lambda.kt
net/println/kt07/LambdaKt$main$2
*L
1#1,28:1
*E

}


// ================META-INF/production sources for module kt07_main.kotlin_module =================


net.println.kt07LambdaKt

Android 也没有问题

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        verticalLayout{
            imageView {
                async {
                    imageBitmap = await{ loadImage(url) }
                }
            }
        }
    }
}

编译成 JavaScript

import kotlin.browser.document

fun main(args: Array<String>) {
    document.writeln("Hello World from Kotlin-js")
}

if (typeof kotlin === 'undefined') {
  throw new Error("Error loading module 'kotlin-javascript'. Its dependency 'kotlin' was not found. Please, check whether 'kotlin' is loaded prior to 'kotlin-javascript'.");
}
this['kotlin-javascript'] = function (_, Kotlin) {
  'use strict';
  function main(args) {
    document.writeln('Hello World from ' + browerInfoString());
  }
  _.main_kand9s$ = main;
  Kotlin.defineModule('kotlin-javascript', _);
  main([]);
  return _;
}(typeof this['kotlin-javascript'] === 'undefined' ? {} : this['kotlin-javascript'], kotlin);

Native 编译与 C 兼容

#ifndef CN_KOTLINER_H
#define CN_KOTLINER_H

void printHello();

int factorial(int n);

#endif

package cn.kotliner.native

import konan.SymbolName
import kotlinx.cinterop.*

@SymbolName("kni_cn_kotliner_native_printHello")
external fun printHello(): Unit

@SymbolName("kni_cn_kotliner_native_factorial")
external fun factorial(n: Int): Int

Kotlin 给我们带来什么

简洁性

data class Customer(
    val name: String, 
    val email: String, 
    val company: String)

数据类

val positiveNumbers = list.filter { it > 0 }

Lambda表达式

单例

object ThisIsASingleton {
    val companyName: String = "JetBrains"
}

异步

async {
    val bitmap = await{ loadImage(url) }
}

安全性

override 关键字

空类型安全

var output: String
output = null   // Compilation error

override fun doTask(){
    ...
}

主构造器

class PhoneCall(val id: String){

    constructor(val id: String, val caller: String): this(id){
        ...
    }
}

通用性

都有谁在用 Kotlin

JetBrains

Kotlin 的诞生地

IntelliJ 全家桶的开发语言

Google

Android 官方开发语言

Square

Jake Wharton 的公司

大神已经贡献了不少 Kotlin 框架

沪江

绝大部分代码已经替换为 Kotlin，是国内较早采用 Kotlin 的公司

花瓣网

Android app 100% 使用 Kotlin 开发

快乐迭代

不要 Java，只用 Kotlin 的公司

Coursera

Android app 部分代码使用 Kotlin 开发

Uber

主要用来开发内部工具，例如Gradle 插件、注解处理器等等

你该不该用 Kotlin

用 Kotlin 开发 Android 靠谱吗？

Google 说，靠谱啊
Jake Wharton 大神早就说，性能没问题，放心大胆地用
国内有不少公司尝试，还没听说不好的
问题：需要与你的协作者沟通好

用 Kotlin 开发服务端靠谱吗？

Spring 说靠谱啊
可直接使用 Java 的框架
纯 Kotlin 框架例如 ktor
问题：跟你的协作者沟通好

Kotlin 会不会慢慢把 Java 取代了？

短期内不会，而且我们也没必要担心这个
不会写 Kotlin 的人倒是可能被 Java&Kotlin 给淘汰掉

Kotlin 学习资料

公众号 Kotlin

周一发文
技术干货
社区动态

Kotlin 中文网

https://www.kotlincn.net/

Kotlin 中文社区

https://kotliner.cn/

Kotlin 中文博客

https://blog.kotliner.cn/

KotlinThree

http://shanghai.kotliner.cn/

视频教程

https://github.com/enbandari/Kotlin-Tutorials

实例展示

Gradle 配置

group 'net.println.kotlin'
version '1.0-SNAPSHOT'

buildscript {
    ext.kotlin_version = '1.1.2-2'

    repositories {
        mavenCentral()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

apply plugin: 'java'
apply plugin: 'kotlin'

sourceCompatibility = 1.5

repositories {
    mavenCentral()
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    testCompile group: 'junit', name: 'junit', version: '4.11'
}

Hello World

**
 * Created by benny on 2/18/17.
 */
fun main(args: Array<String>) {
    println("Hello World")
}

when 表达式

fun main(args: Array<String>) {
    val x = 5
    when(x){
        is Int -> println("Hello $x")
        in 1..100 -> println("$x is in 1..100")
        !in 1..100 -> println("$x is not in 1..100")
        args[0].toInt() -> println("x == args[0]")
    }

    val mode = when{
        args.isNotEmpty() && args[0] == "1" -> 1
        else -> 0
    }.let(::println)
}

try-catch 表达式

fun main(args: Array<String>) {
    val result = try{
        args[0].toInt() / args[1].toInt()
    }catch (e: Exception){
        0
    }
    println(result)
}

输入：100 50

扩展方法

fun main(args: Array<String>) {
    println("*" * 16)
}

operator fun String.times(int: Int): String{
    val stringBuilder = StringBuilder()
    for(i in 0 until int){
        stringBuilder.append(this)
    }
    return stringBuilder.toString()
}

数据类

data class Country(val id: Int, val name: String)

fun main(args: Array<String>) {
    val china = Country(0, "中国")
    println(china)
    println(china.component1())
    println(china.component2())
    val (id, name) = china
    println(id)
    println(name)
}

科里化

fun <P1, P2, P3, R> Function3<P1, P2, P3, R>.curried()
    = fun(p1: P1) = fun(p2: P2) = fun(p3: P3) = this(p1, p2, p3)

fun log(tag: String, target: OutputStream, message: Any?){
    target.write("[$tag] $message\n".toByteArray())
}

fun main(args: Array<String>) {
    log("benny", System.out, "HelloWorld")
    ::log.curried()("benny")(System.out)("HelloWorld Again.")
}

HTML DSL

fun main(args: Array<String>) {
    html {
        "id"("HtmlId")
        "head"{
            "id"("headId")
        }
        body {
            id="bodyId"
            `class` = "bodyClass"

            "a"{
                "href"("https://www.kotliner.cn")
                +"Kotlin 中文博客"
            }
        }
        "div"{ }
    }.render().let(::println)
}

Gradle DSL

group = "cn.kotliner.kotlin"
version = "1.0-SNAPSHOT"

buildscript {
    extra["kotlin_version"] = "1.1.2"

    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:${extra["kotlin_version"]}")
    }
}

apply {
    plugin("java")
    plugin("kotlin")
}

configure<JavaPluginConvention>{
    setSourceCompatibility(1.5)
}

repositories {
    mavenCentral()
}

dependencies {
    compile("org.jetbrains.kotlin:kotlin-stdlib-jre8:${extra["kotlin_version"]}")
    testCompile("junit", "junit", "4.12")
}

协程

frame.onButtonClick {
    log("协程之前")
    我要开始协程啦(DownloadContext(LOGO_URL)) {
        log("协程开始")
        try {
            val imageData = 我要开始耗时操作了 { 
                我要开始加载图片啦(this[DownloadContext]!!.url) 
            }
            log("拿到图片")
            frame.setLogo(imageData)
        } catch(e: Exception) {      ...      }
    }
    log("协程之后")
}

Android-Support

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)

        fab.onClick { view ->
            Snackbar.make(view!!, 
                    "Replace with your own action", 
                    Snackbar.LENGTH_LONG)
                .setAction("Action", null).show()
            helloWorld.text = "${System.currentTimeMillis()}"

            startActivity<Main2Activity>("Key" to "From MainActivity")
        }
    }
}

Android-Support

class Main2Activity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        relativeLayout {
            textView(intent.extras["Key"]?.toString()?: "Hello") {

            }.lparams(matchParent, matchParent){
                gravity = Gravity.CENTER
            }
        }
    }
}

JavaScript-Support

fun main(args: Array<String>) {
    document.getElementById("title")?.innerHTML = "Hello World from Kotlin!!"
    val canvas = document.getElementById("myCanvas") as HTMLCanvasElement
    val cxt=canvas.getContext("2d") as CanvasRenderingContext2D
    cxt.fillStyle ="#ffffff"
    cxt.strokeStyle = "#FF0000"
    cxt.moveTo(canvas.width / 2.0, canvas.height / 2.0)
    canvas.onclick = { event ->
        if(event is MouseEvent){
            cxt.clearRect(0.0, 0.0, canvas.width.toDouble(), canvas.height.toDouble())
            cxt.lineTo(event.offsetX, event.offsetY)
            cxt.stroke()
        }
    }
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Hello World Kotlin</title>
</head>
<body>
<h1 id="title">Title</h1>
<canvas id="myCanvas" width="1000px" height="500px"></canvas>
</body>
<script type="text/javascript" src="out/production/kotlin-javascript/lib/kotlin.js"></script>
<script type="text/javascript" src="js/browserinfo.js"></script>
<script type="text/javascript" src="out/production/kotlin-javascript/kotlin-javascript.js"></script>
</html>

JavaScript-Support

Native-Support

#include "cn_kotliner.h"
#include <stdio.h>

void printHello(){
    printf("[C] HelloWorld\n");
}

int factorial(int n){
    printf("[C] calc factorial: %d\n", n);
    if(n == 0) return 1;
    return n * factorial( n - 1 );
}

import cn.kotliner.native.*

fun main(args: Array<String>){
    printHello()
    (1 .. 5).map(::factorial).forEach(::println)
}

Native-Support

Q&A

遇见 Kotlin

By 霍丙乾

遇见 Kotlin

Kotlin 是一门静态语言，兼容 Java，运行在 JVM、Android、以及浏览器上。

2,611

霍丙乾

腾讯 Android工程师，Kotlin布道师。公众号 Kotlin ，网站：https://www.kotliner.cn

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可以跑在Java 虚拟机上

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都有谁在用 Kotlin

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快乐迭代

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when 表达式

try-catch 表达式

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